Python Raise Keyword

In this article, we will learn how the Python Raise keyword works with the help of examples and its advantages.

Python Raise Keyword

Python raise Keyword is used to raise exceptions or errors. The raise keyword raises an error and stops the control flow of the program. It is used to bring up the current exception in an exception handler so that it can be handled further up the call stack.

Python Raise Syntax

raise  {name_of_ the_ exception_class}

The basic way to raise an error is:

raise Exception(“user text”)

Checking whether an integer is odd or even

In the below code, we check if an integer is even or odd. if the integer is odd an exception is raised.  a  is a variable to which we assigned a number 5, as a is odd, then if loop checks if it’s an odd integer, if it’s an odd integer then an error is raised.

Python3

a = 5

if a % 2 != 0:
    raise Exception("The number shouldn't be an odd integer")

Output:

Checking Errror Type

We can check the type of error which have occurred during the execution of our code. The error can be a ‘ValueError’ or a ‘ZeroDivisionError’ or some other type of error.

Syntax: raise TypeError

Checking the error type

In the below code, we tried changing the string ‘apple’  assigned to s to integer and wrote a try-except clause to raise the ValueError. The raise error keyword raises a value error with the message “String can’t be changed into an integer”.

Python3

s = 'apple'

try:
    num = int(s)
except ValueError:
    raise ValueError("String can't be changed into integer")

Output

Raising an exception Without Specifying Exception Class

When we use the raise keyword, there’s no compulsion to give an exception class along with it. When we do not give any exception class name with the raise keyword, it reraises the exception that last occurred.

Example

In the above code, we tried changing the string ‘apple’ to integer and wrote a try-except clause to raise the ValueError. The code is the same as before except that we don’t provide an exception class, it reraises the exception that was last occurred.

Python3

s = 'apple'

try:
    num = int(s)
except:
    raise

Output:

Advantages of the raise keyword

• It helps us raise error exceptions when we may run into situations where execution can’t proceed.
• It helps us raise error in Python that is caught.
• Raise allows us to throw one exception at any time.
• It is useful when we want to work with input validations.